Anatomy of the Eye Flashcards
What are the 6 oculomotor muscles that allow rotation of the ocular bulb?
- lateral rectus: outward horizontal movement
- median rectus: horizontal movement towards medial line of body
- superior rectus: upward movement
- inferior rectus: downward movement
- inferior oblique: downward outer rotation
- superior oblique: upward external rotation
How are the eyes connected to the encephalon (brain)?
via the optic nerves
What are the 3 fluid filled spaces within an eye?
ANTERIOR CHAMBER
Located between cornea and iris.
Contains aqueous humour.
POSTERIOR CHAMBER
Located between iris and lens.
Contains aqueous humour.
VITREOUS CHAMBER
Located posterior to the lens, between the lens and the posterior wall/retina of the eye
Contains vitreous humour.
What are the components of the ‘outer fibrous tunic’ of the eye?
= external membrane, which is divided into”
- CORNEA: anterior aspect, which lacks blood vessels and lymphatic vessels.
- SCLERA: posterior aspect. Poorly vascularised
What is the palpebral fissure?
oval shaped space between the medial and lateral canthi of the eye lids
How does the upper eye lid differ to the lower lid?
- bigger
- more mobile
What are the medial and lateral canthi?
corners of the eye lids
What is lacrimal caruncle?
globular nodule at the medial canthus
made of skin covering sebaceous and sweat glands
What is the location and function of the lacrimal gland?
located near the lateral canthus superiorly
it is where tears are produced and secreted to the surface of the globe via the lacrimal dict
What is the lacrimal papilla?
small, fleshy projection of the margin of each eyelid close to the medial canthus
Opening of the papilla: PUNCTUM
What is the function of the lacrimal punctum?
opening of the papilla
where tears are collected and travel through the superior and inferior lacrimal canaliculi to the lacrimal sac
Where does the lacrimal sac drain to?
contains tears
drains to the inferior nasal meatus through the naso-lacrimal duct (“runny nose”)
Where is the tough sclera located?
part of the fibrous layer of the globe
Why might loss of sympathetic innervation cause mild drooping (ptosis) of the eyelid?
Ptosis is mild as innervation only lost to the smooth muscle aspect of LEVATOR PALPEBRAE SUPERIORIS muscle
(~30% of its fibres)
What is the other name for the Levator superioris muscle?
Müller’s muscle
Why might more of the sclera be visible during anxiety or in hyperthyroidism?
increased activity in Müller’s muscle via the sympathetic fibre (stimulation)
=> wide eyes
What is the bony orbit?
dry skull
Which bones are contained within the bony orbit?
- frontal
- zygomatic
- maxillary
- lacrimal
- ethmoid
- sphenoid
What does the optic canal transmit?
CN II (optic nerve)
What does the superior orbital fissure transmit?
CN III (oculomotor nerve) CN IV (trochlear nerve) CN V1 (branch one of trigeminal nerve: ophthalmic nerve) CN VI (abducens nerve)
What are the 12 cranial nerves?
OLFACTORY (CN I)
OPTIC (CN II)
OCULOMOTOR (CN III)
TROCHLEAR (CN IV)
TRIGEMINAL (CN V)
ABDUCENS (CN VI)
FACIAL (CN VII)
VESTIBULOCOCHLEAR (CN VIII)
GLOSSOPHARYNGEAL (CN IX)
VAGUS (CN X)
ACCESSORY NERVE (CN XI)
HYPOGLOSSAL (CN XII)
How many degrees does the eye need to be adducted by in order for the visual and anatomical axes to coincide?
pupil needs to be adducted at ~22.5 degrees
this is from its neural position to make the visual axis (line of sight) coincide with the anatomical axis
What is an orbital “blowout” fracture?
usually follows energetic impact to the anterior globe
this causes a sharp increase in infraorbital pressure
fracturing the thin bony plates of the orbital walls
What is the globe of the eye surrounded by?
periorbital fat
What are the 3 layers of the eye?
- fibrous
- vascular
- neural
what is the outer layer of the eye composed of?
tough, collagen-rich fibrous tissue
What makes up the outer layer of the eye?
(fibrous tunic = outer layer)
- sclera
- cornea
What is the cornea?
a transparent, protective layer covering the iris and pupil
What is the fibrous tunic layer continuous with ?
the dural sheet - covers the optic nerve
where the optic nerve emerge from the globe?
the posterior-medial aspect of the globe
What are the components of the vascular tunic?
- choroid
- ciliary body
- iris
What is the function of the choroid?
provides O2 and nourishment to the outer layers of the retina
What is the function of the ciliary body?
CILIARY MUSCLE
controls the shape of the lens
CILIARY EPITHELIUM
produces the aqueous humour
What is the function of the iris?
controls the diameter and size of the pupil
and therefore the amount of light reaching the retina
What dos the uveal tract refer to?
components of the vascular tunic (choroid, iris, and ciliary body)
What is the importance of the pigmentation within the choroid?
melanin helps the choroid to limit uncontrolled reflection whin the eye
this would result in perception of confusing images
What is the function of the retina?
receives light that the lens has focused
then converts the light into neural signals and sends them to the brain for interpretation
What is the macula lutea?
= yellow spot
FOVEA: contained within the macula is a small central pit used for central vision like reading
- important for high acuity, central vision
Where is the physiological blind spot?
at the optic nerve head (optic disc)
What type of photoreceptors are usually affected to affect night vision?
=> Rods
night blindness: nyctalopia (usually occurs due to retinitis pigmentosa)
What are RODS important for?
- work well in low-light (scotopic)
- important for night vision
- more important for peripheral vision
- detection of moving objects
What are CONES important for?
- in stronger light (photopic)
- provide colour vision
- for fine details (e.g. reading)
- much more abundant in the central area of retina
Where are CONES most numerous?
central retina:
- macular lutea
- fovea centralis
What is uveitis?
inflammation of the uveal tract
What is irodocyclitis?
inflammation of iris and the ciliary body
inflammation is predominately confined to the ciliary body
Where is the lens located?
nestled in the hyaloid fossa
bowl shaped depression in the anterior surface of the vitreous body
What is the vitreous body?
clear gel that fills the space between the lens and the retina
How do the anterior and posterior curvatures of the lens differ?
anterior surface is less curved that the posterior
What causes flattening of the anterior surface of the lens?
tension in the ciliary zonule
What is the length of the normal eye in adulthood?
24 mm
How does myopia relate to eye length?
short sightedness die to a long eyeball (>24mm)
What is the nature of aqueous humour?
- similar to blood plasma
- but with low protein concentration
- helps to maintain the intraocular pressure
- maintains spherical shape of the eye
Where is aqueous humour reabsorbed?
the sinus venosus
= canal of Schlemm
What is the normal intraocular pressure?
~ 16-21 mmHg
What the fundus of the eye refer to?
back of the inside of the eye
includes the retina and optic nerve
What feature seen on fundoscopy would suggest raised intraocular pressure?
enlargement of the optic cup (cup-like hole in middle of optic disc)
What is the clinical significance of the cup-to-disc ration in eye disease?
measure of used in Dx of glaucoma
How do fibres from the retina travel to the optic chiasm?
fibres from the nasal/inside half of each retina cross to the opposite side of the optic chiasm
this means that info from the RHS of the visual field goes to the LHS of the brain (+vice versa)
If a patient has a right sided hemianopia, how is the lesion located relative to the optic chiasm?
= field defect
lesion must be posterior to the optic chiasm
only a problem localised to one eye (monocular visual defect) can be located anterior to the chiasm
What does the trochlear nerve supply?
only the superior oblique muscle
therefore nerve is v. thin
Where does the abducens nerve arise?
between the pons and medullary pyramid
What kind of innervation does the oculomotor provide?
PNS innervation to the eye
Which 2 structures receive PNS stimulation from the oculomotor nerve?
SPHINCTER PUPILLAE
constricts the pupil, reducing the amount of light entering the eye
CILIARY MUSCLES
contracts causing the lens to become more spherical (better for short distance vision)
What are the 2 pupil reflexes of the eye?
- light reflex
- near reflex
What 3 components make up the accommodation reflex?
- pupillary constriction
- medial convergence of the eyes
- focusing of the eyes on a near object (required contraction of ciliary muscles and bulging of the lens)
Which muscles cause medial convergence of the eyes?
medial recti muscles
Why is a sudden dilation of one pupil a concern in someone with a head injury?
oculomotor nerve is closely related to the free edge of the tentorium
this can get compressed
the PNS fibres (pupilloconstrictor) are locals at the peripheral part of this nerve -> pupil size is affected
What are the 2 main types of third nerve palsy?
Third nerve = CN III = oculomotor nerve
- SURGICAL: due to mechanical compression
- MEDICAL (diabetic for e.g.) causes ischaemia
this is pupil sparing - since the pupilloconstcitr fibres are at the periphery and therefore better perfused
unlike the oculomotor at fibres located centrally
